Question: The mean life of a battery used in a digital clock is 305 days. The lives of the batteries follow the normal distribution. The battery was recently modified to last longer. A sample of 20 of the modified batteries had a mean life of 311 days with a standard deviation of 12 days. You have been asked to test if the modifications have increased the mean life of the batteries at the .05 significance level.
a) State the null & alternative hypothesis:
b) Compute the test statistic and indicate your decision regarding the null hypothesis? Hint: First determine your decision rule.